Automotive supplemental inflatable restraint systems, such as airbag cushion restraint systems, have conventionally employed pyrotechnic inflators, such as inflators containing azide-based gas-generating compositions, to provide inflation gases for inflating the airbag cushion. While pyrotechnic based inflators have provided acceptable airbag inflation, such systems are not without their drawbacks and disadvantages. For example, ignition and burning of the pyrotechnic gas-generating materials produces undesirable hot particulate by-products which can cause damage to the airbag or a vehicle occupant. A considerable amount of effort has gone into producing a pyrotechnic based airbag inflation system in which the inflator traps generated hot particulate material within the inflator body itself so that it cannot escape to damage the airbag. Also, considerable effort has gone into attempts to eliminate the production of such hot particulate materials. Additionally, such pyrotechnic gas-generating compositions pose a problem due to the toxicity of the gas produced.
More recently it has been proposed to replace such pyrotechnic based inflation system with hybrid inflators in which the main proportion of the inflation gases is provided by stored pressurized gas in the inflator. However, such hybrid inflators generally still require the presence of pyrotechnic materials (albeit in a reduced amount) in order to provide ignition and thereby provide supplemental inflation gases and to heat the pressurized stored gas in order to arrange for the release of the stored gas, such as, for example, by providing means or additional pressure to rupture burst disks in the inflator to release the stored pressurized gas.
Even more recently it has been proposed, in co-pending application Ser. No. 08/423,261, filed Apr. 17, 1995, and assigned to the Assignee of this Application, to provide a co-flow hybrid type inflator in which a heat-producing but non gas-producing composition, such as a thermite composition, is ignited by an ignitor material (such as boron potassium nitrate). Stored pressurized gas is caused to flow over and/or through the exothermic thermite reaction product to produce heated pressurized gas sufficient to effectively inflate an inflatable airbag restraint cushion. Such a co-flow hybrid inflator employing a thermite composition is disclosed in FIGS. 6 to 9 and the description at pages 8 to 13 of said co-pending Application.
The aforementioned co-pending Application mentions the use of a thermite composition of aluminum metal fuel and iron oxide oxidizer with the possible addition of supplemental oxidizing agent potassium perchlorate as a burn enhancer. However, it has been discovered that attempts to produce inflators employing such thermite compositions as a non gas-producing heat source for stored pressurized gas in such a co-flow hybrid inflator have not been entirely successful. It has been proposed to form the thermite compositions into extruded pellets, wafers, tablets, grains or the like for use in such co-flow hybrid inflators. However, these extruded forms of the thermite compositions are prone to form dust or powder upon initiation and gas blow-by which prevents complete reaction of the thermite since the thermite dust or powder is carried out of the inflator. Moreover, such extruded forms of thermite compositions can produce undesirable hot particulate matter which can escape from the inflator and be detrimental to the airbag. Another problem encountered with the extruded thermite compositions is the inability to obtain a generally acceptable burn rate. Additionally, such extruded thermite compositions have been found to be very difficult to ignite. Moreover, the temperature needed to ignite the extruded thermite compositions has been undesirably high.
It is therefore desirable to provide an improved form of heat-producing, non gas-producing compositions, particularly thermite compositions, for use in motor vehicle airbag inflators which compositions are more easily ignited and have an increased burn rate. It would also be desirable to provide an improved form of such compositions which enable substantially all the compositions to be ignited and burned within the inflator and to do so without producing substantially any unburned dust or powder or hot particulate matter that can be carried out of the inflator. It is also desirable to provide such improved form of such compositions which are able to ignite at an acceptably low ignition temperature, for example, at a temperature of about 2000.degree. C. or less. It is also desirable to provide an improved form of such compositions of the aforesaid properties and characteristics which compositions still generate heat producing chemical reactions generating little or no gas to augment the performance of stored pressurized gas hybrid inflators and yet still increases the temperature and performance of the stored pressurized gas inflator due to the heat generating characteristics of the improved compositions. It would also be highly desirable if such improved form of such compositions would not produce any significant hot particulate by-product materials. It is also desirable if such improved form of such compositions could be provided with the foregoing characteristics and yet be able to ignite at an acceptably low ignition temperature while still provide inflation performance essentially equivalent to a standard pyrotechnic--stored gas hybrid inflator.